A power amplifier includes a driver stage and a power stage. The driver stage is used to amplify an input signal in advance ahead of the power stage so that the maximum output is obtained at the power stage. In this case, there is a need for a power voltage VDD to amplify an input signal, but when a power amplifier is composed of a driver stage and a power stage, the amplification gains are different at the stages, so it is required to separately supply power voltages.
FIG. 1 is a circuit diagram of a multistage power amplifier 100 of the related art. Referring to FIG. 1, the multistage power amplifier 100 of the related art includes a first driver stage 110, a second driver stage 120, and a power stage 130. In this case, the first driver stage 110 amplifies a first signal inputted through an input terminal 111 and outputs a second signal that is the amplified first signal to an input terminal 121, which is connected with an output terminal 114, of the second driver stage 120. The input terminal 121 of the second driver stage 120 is connected with the output terminal 114 of the first driver stage 110 and receives and amplifies the second signal and outputs a third signal that is the amplified second signal to an input terminal 131, which is connected with the output terminal 124, of the power stage 130. The power stage 130 amplifies the third signal inputted from the output terminal 124, which is connected with the input terminal 131, of the second driver stage 120 and outputs a fourth signal that is the amplified third signal through an output terminal 134.
In general, the first driver stage 110 and the second driver stage 120 require a low output power in comparison to the power stage 130. Accordingly, the multistage power amplifier 100 in which the first driver stage 110, the second driver stage 120, and the power stage 130 are connected in a cascade type, different power voltages are applied to the power input terminals 112 and 122 of the first driver stage 110 and the second driver stage 120 and the power input terminal 132 of the power amplifier 130, and their ground terminals 113, 123, and 133 are all grounded, has been developed. In this configuration, since the power voltage applied to the first and second driver stages 110 and 120 and the power voltage applied to the power stage 130 are different, there is a need for a specific regulator, so it reduces power efficiency, complicates an integrated circuit, and reduces the design area of the integrated circuit.
The background art of the present invention has been described in Korean Patent No. 10-0775942 (Nov. 6, 2007).